Cerberus

Cerberus or Kerberos, (Greek form: Κέρβερος, [ˈkerberos]) in Greek and Roman mythology, is a multi-headed (usually three-headed) dog, or "hellhound" with a serpent's tail, a mane of snakes, and a lion's claws. He guards the entrance of the underworld to prevent the dead from escaping and the living from entering. Cerberus is featured in many works of ancient Greek and Roman literature and in works of both ancient and modern art and architecture, although the depiction of Cerberus differs across various renditions. The most notable difference is the number of his heads: Most sources describe or depict three heads; others show Cerberus with two or even just one; a smaller number of sources show a variable number, sometimes as many as 50 or even 100.

In most works, the three heads each respectively see and represent the past, the present, and the future, while other sources suggest the heads represent birth, youth, and old age. Each of Cerberus' heads is said to have an appetite only for live meat and thus allow only the spirits of the dead to freely enter the underworld, but allow none to leave.Cerberus was always employed as Hades' loyal watchdog, and guarded the gates that granted access and exit to the underworld.